Maintaining the integrity of a cable that drives a cable car along a pathway can be an expensive and labor intensive process which is prone to error. Cable inspection is a manual process that is performed through repeated shifts of human inspectors standing watch inside a cable car motor building. The tedious task of inspectors includes observing the cable as it moves past an observation area, with the inspectors looking for a critical part of the cable known as the splice to appear. For the length of cable used by the San Francisco cable car lines, this can take between 10-35 minutes of waiting and much longer if the splice is missed by the inspector. It is also difficult or impossible to see small defects in the cable with even a trained human eye since the cable is moving rapidly (e.g., 10 mph) past the inspector.
Human inspectors are inherently prone to error and limited by constraints of human vision and visual analysis (even for a trained eye). Human inspectors are also subject to fatigue and can be distracted, missing even large defects in the moving cable. Moreover, without stopping movement of the cable, human inspectors have a very limited ability to consistently assess relative defect levels in the moving cable and may not be capable of adequately assessing and/or reporting observed defects which are only momentarily observed as the cable moves at relatively high speed and are not suited for accurately evaluating changes in defects over time.